1. Field of the Invention
The present invention relates to chloroprene rubber latex for an adhesive containing, as an ingredient, a chloroprene rubber polymer. More specifically, it relates to a chloroprene rubber latex for an adhesive containing a polymer which, when dissolved in chloroform to a concentration of 10% by weight, provides a solution which does not contain organic solvent insolubles and which has a solution viscosity of 100 mpa.multidot.s to 6000 mpa.multidot.s, having an excellent room temperature bonding strength, high temperature bonding strength, water resistance, and other bonding properties and latex stability, and having these bonding properties balanced at a high level.
2. Description of the Related Art
Processes for the production of chloroprene rubber polymer latexes comprised of chloroprene and a carboxyl-group containing vinyl monomer such as acrylic acid or methacrylic acid are known from Japanese Unexamined Patent Publication (Kokai) No. 61-12710, Japanese Unexamined Patent Publication (Kokai) No. 62-257918, etc. Further, processes for production of latexes for adhesives using a water-soluble polymer such as a polyvinyl alcohol as an emulsifying and dispersing agent and adhesives using the same are known in Japanese Examined Patent Publication (Kokoku) No. 52-13983, Japanese Examined Patent Publication (Kokoku) No. 61-29968, etc.
However, there have been the following problems when using a chloroprene rubber latex produced by these processes.
(1) In the conventional latexes for adhesives, when increasing the molecular weight to improve the heat resistance, the tack retention (or adhesion retention) and room temperature bond strength were decreased and it was not possible to obtain physical properties sufficient for an adhesive. Further, attempts were made to improve the heat resistance by cross-linking the carboxyl-group containing vinyl monomer etc. with a metal oxide. However, it was not possible to achieve the physical properties expected due to the protective colloidal nature of the emulsifying agent used.
(2) When using an emulsifying agent having an excellent latex stability in the high pH region such as an alkaline metal salt of a rosin acid for the production, the rubber precipitates due to the slight changes in the pH when adding the tackifier, metal oxide, and other secondary components required for a chloroprene adhesive, and therefore, it is necessary to control the pH extremely carefully, which makes the procedure complicated. Further, when using a water-soluble polymer such as a polyvinyl alcohol for the production, a superior latex stability is exhibited due to the protective colloidal nature. However, since the polymer is water-soluble, the water resistance is remarkably degraded when used as an adhesive.